Zinc-base die-casting alloy



Patented Apr. 5, 1932 UNITED STATES PATENT OFFICE}.

EDIUND A. ANDERSON AND GEORGE L. W'ERLEY, F PALMEfiTON, PENNSYLVANIA,

ASBIGNORS TO THE NEW JERSEY ZINC COMPANY, OF NEW YORK, N. Y., A 003-ronarron on NEW JERSEY ZINC-BASE DIE-CASTING- ALLOY Ho Drawing.

This invention relates to zinc base die-casting alloys and has for itsobject the provision of an improved alloy of this character.

The mechanical requirements of the diecasting operation necessitate theconstruction of the melting pot and die from iron and steel. Thesemetals are subject to attack by molten zinc and it has been found fromexerience that at least 0.25% aluminum must e added to the zinc in orderto minimize this attack sufficiently to secure reasonable life from theapparatus. Alloys for die-casting must possess a sutficient degree offluidity to properly flow into and completely fill the it dies used, and2% or more aluminum appears to be necessary to secure an adequate degreeof fluidity. It has also long been known that aluminum increases thetensile strength of zinc and this, in itself, makes its presence in zincbase die-casting'alloys desirable in quantities of form 2% to as much as10 to 15%.

Zinc-aluminum alloys containing less than about 80% of aluminum undergoa structural change subsequent to solidification which is during thecooling of the alloy after casting or may through certain influences beretarded or inhibited. In such cases it may take place gradually over aperiod of months in at ordinary temperatures.

A secondary stage of phase change which sometimes occurs is the growthor coalescence of the extremely small particles of the new bases asfirst formed into larger particles. This stage may be accompanied bysoftening Application filed August 21, 1930. Serial 1W0. 476,946.

aussuEn and lowering of tensile strength and by an increase in ductilityand impact strength.

Zinc-aluminum alloys in this range of composition are also subject to atype of disintegration commonly known as intercrystal- 4, lineoxidation. In extreme cases, under the influence of warmth and moisture,intercrystalline oxidation may'completely penetrate specimens of thesealloys and cause swelling, warping and even complete disintegration. tIntercrystalline oxidation is in some way associated with and partlydependent upon the phase change.

It has heretofore been recognized that certain other metals when presentin these zinc-aluminum alloys exercise important effects on either thephase change or the intercrystalline oxidation or both. For example,copper and magnesium are known to exert an influence on the phase changeeither 1 5 in respect to the rate at which it takes place .or thecompleteness of the reaction or in some other respect not fullyunderstood. The particular efl'ect produced by copper and magnesiumonthe phase change reacts favorably in increasing the resistance of thealloys to intercrystalline oxidation. Lead, while not exerting anymarked influence on the phase change, very seriously diminishes theresistance of these zinc-aluminum alloys to intercrystalline oxidation.Cadmium, though having a certain effect on the phase change, in thepresence of lead usually diminishes the resistance of these alloys tointercrystalline oxidation. so

In the course of an exhaustive investigation of zinc base die-castingalloys, we have found that the tendency of zinc-aluminum alloys toundergo intercrystalline oxidation is greatly diminished by theelimination of harmful im- 55 August 17th, 1926, by the use of highgrade zinc metal (e. g. horsehead brand) as the zinc base of the alloy.High grade zinc metal, however, contains as much as 0.05% of lead and toproduce an alloy sufliciently free from intercrystalline oxidation withthis amount of lead present, additions of both copper and magnesium arenecessary since these metals individually tend to retard or preventintercrystalline oxidation and when present together have a more or lessadditive beneficia effect. 1

Continued experiments with zinc metal con taining materially less leadthan present in high grade zinc metal indicated definitely that therewere important possibilities in this direction. The first importantdiscovery was that if-the percentage of lead and other impurities in thezinc metal (used in making up the zinc base alloy) was less than 0.02%,with tin substantially absent, the presence of 0.1% magnesium in analloy containing 4% aluminum (and without copper) was suflicient toprevent intercrystalline oxidation, and that such an alloy had otherdesirable physical properties. The advantage gained by the eliminationof copper from this alloy was primarily an increased impact strengthwith better retention of this impact strength upon ageing either at roomtemperature or elevated temperatures. This discovery constitutes thebasis of a copending patent application, Serial No. 368,730, filed June5, 1929 (which has since issued into United States Patent No. 1,779,525,of October 28, 1930). However, the elimination of copper from the 4%aluminum, 3% copper, 0.1% magnesium alloy resulted in a lower tensilestrength which under some circumstances, might make the alloy lessvaluable.

We next discovered that it was-not necessary to entirely eliminate thecopper in order to obtain the advantageous characteristics of thelast-mentioned alloy. On thecontrary, we found that additions of copperup to 1% are accompanied by slightly improved tensile strengthapparently without any corollary disadvantages. This discovery forms thebasis of our copending patent application Serial No. 476,452; filedAugust 19, 1930.

Our present invention is based on the discovery that in an alloy madewith zinc metal of high purity and containing aluminum, for example 4%,the presence of a small amount r of copper (without magnesium), forexample 1%, is sufiicient to give substantially complete resistance tointercrystalline oxidation. As compared with the 4% aluminum, 0.1%magnesium zinc base alloy (without copper), made with the same grade ofhigh purity zinc metal, the alloy containing 4% aluminum and 1% copper(without magnesium) has the advantage of a higher initial impactstrength with a somewhat higher impact strength after ten days exposureto air saturated with moisture at 95 C.

The new alloy also has an appreciably higher ance zinc metal of highpurity containing 9999+ zinc. The zinc metal of high purity shouldcontain not more than about 0.01% lead plus cadmium. Very satisfactoryresults have been secured with zinc metal containing 99.99+% zinc, lessthan 0.003% lead, less than 0.003% cadmium and less than 0.001% tin. Tinshould be substantially excluded from the alloy and in no case shouldthe tin content exceed about 0.001%.

The following tables illustrate the important physical properties ofdie-castings made of an alloy of the invention. Alloy No. 1 is of thecomposition described in United States Patent No. 1,596,761; alloy No. 2is of the composition disclosed in my copending patent applicationSerial No. 368,730, alloy No.

-3 is of the composition disclosed in my copending patent applicationSerial No. 476,452; filed August 19, 1930; and alloy No. 4 is of thecomposition embraced within the present invention.

Composition 1 Alloy No. 1 41loyNo.2 Alloy No.3 g a 4 Pat. .N. 368,730 s.N. 476,452 1,596,761

Aluminum 4. 0% 4.0% 4. 0% 4.0% Copper 3. 0% 1. 0% 1. 0% Magnesium 0.1% v0.1% p 0.1% Quality of zinc H i g h High puri- High puri- High puribase.grade ty 99.99% ty 99.99% ty 99.99%

Zn. Zn. Zn.

Properties as cast Tensile strength 46, 200 39, 400 42, 700 40. 800Tensile strength round 45, 600 37,300 43,100 41,800 Impact strength" 108130 169 288 Properties after ten days in steam at 95 C.

Tensile strength i] 27,800 31,600 33,400 34, 500 Tensile strength round32, 800 31, 900 34, 400 36, 000 Impact strength" 8 142 137 170 Expansionwide 0. 0076 0. 0012 0. 0008 0 0006 Expansion $6" wide 0. 0068 0. 00160. 0006 0. 0007 The tensile strength is indicated in pounds per squareinch forflat and round test specimens. The impact strength is indicatedin foot pounds per square inch. Linear expansion is indicated in inchesin; test sections in. and V in. in width.

We claim: 7

1. A zinc base alloy consisting of about 4% aluminum, about 1% copperand the balance zinc metal of high purity with at least 99.98% v 2. Azinc base alloy consisting of 2 to 5% aluminum, 0.05 to 2% copper, andin which the zinc base is zinc metal of high purity containing at least99.98% zinc.

In testimony whereof we afiix our signatures.

EDMUND A. ANDERSON. GEORGE L. WERLEY.

